1. Field of the Invention
The present invention relates to a vinyl chloride resin composition having thermal expandability, and relates more particularly to a thermally expandable vinyl chloride resin composition and a molded article thereof which exhibit excellent thermal expandability, excellent shape retention following expansion of the molded article, and for which continuous molding by extrusion molding or calender molding or the like can be conducted with ease.
2. Description of the Prior Art
In the field of building materials, the fire resistance of materials in the case of fire has always been considered important. Recently, a variety of different resins have been used to develop resin materials with fire resistance properties. Desirable fire resistance properties include not only resistance to combustion for the resin material itself, but also an ability of the material to resist collapse and maintain its shape to form an insulating layer, thereby blocking flames and smoke, even when the material is exposed to high temperatures during a fire. Examples of proposed materials that are capable of forming an insulating layer include a material that uses an epoxy resin as the base resin and a thermally expandable graphite as a foaming agent (see patent reference 1), and a material that uses a vulcanized rubber as the base resin (see patent reference 2). However, these materials are produced mainly by batch production methods such as press molding, and because they are unsuited to continuous production by extrusion molding or the like, the productivity tends to be poor.
A material that utilizes the flame retardancy and moldability of a polyvinyl chloride resin, and comprises a polyvinyl chloride resin, a thermally expandable graphite, an inorganic filler and a phosphorus compound, has also been proposed (see patent reference 3). This material exhibits favorable fire resistance, but because it requires the addition of a large quantity of additives, and because the phosphorus compound such as ammonium polyphosphate tends to adhere to metal during processing, molding of the material is difficult, which tends to result in poor productivity.
[Patent Reference 1] Japanese Laid-open publication (kokai) No. 2003-64209
[Patent Reference 2] Japanese Laid-open publication (kokai) No. 2003-226772
[Patent Reference 3] Japanese Laid-open publication (kokai) No. Hei 10-95887